The present application relates to a dynamic quantity detecting member detecting a dynamic quantity such as displacement, force, and acceleration in a capacitance manner and a dynamic quantity detecting apparatus suitable for an input apparatus of an electronic apparatus or the like.
In the past, a keyboard and a switch such as a pressing button switch were widely used as a general input apparatus for an electronic apparatus or the like, that is, an input user interface (UI). In general, the operation of the switch including a remote controller and a mouse is an alternative operation of selecting ON or OFF by physical contact. The UI may considerably damage operability and also restrict the design of an electronic apparatus, since the number of buttons or keys increases as an increase in input information and options are increased.
In recent years, by permitting a pointing device such as a mouse, a touch pad, or a touch screen to be compatible with an output UI, a graphical UI (GUI) enabling an intuitive operation has been widely used.
Through clicking of a pressing button switch, a mouse has a distinguishing feature of being comfortable to operate. However, since the mouse has to be moved on an operating surface, the mouse may not be used in an environment where an operating surface is not provided.
Numerous touch sensing devices, such as touch pads or pen tablets, of a resistance film type, a capacitance type, and a surface elastic wave type have been put to practical use. Moreover, the touch sensing devices have been mounted in an automated teller machine (ATM), various portable information terminals, a car navigation system, and the like. In a general touch sensing device, however, at one operating point the choice of only selecting ON or OFF is enabled, and thus it is difficult to perform complex information processing. Therefore, when there is a lot of information to be processed, the touched surface has to be expanded two-dimensionally. For this reason, the operability may deteriorate and, as with switch, the design of an electronic apparatus is also restrained. Moreover, since there is no clicking sense in the touch sensing device, unlike the pressing button switch, an intuitive operation may not be performed and it is easy to feel an operation is awkward. Moreover, it becomes difficult for the visually impaired to perform an operation, or to perform an operation in a dark place without fumbling.
In order to input more various kinds of information in comparison to the alternative operation, a method of detecting input or displacement during input may be taken into consideration. Various input sensors of a resistance wire type, a piezoelectric type, and the like have been put to practical use as an apparatus sensing pressure. A pen inputting apparatus realizing input information control by reflection of pen pressure during input by providing a pressure sensor in a switching device been appeared. In a generally used pressure sensor, however, the input is converted into an electric signal by receiving the pressure of a pressure source via a diaphragm formed by a metal thin plate or a thin plastic film and detecting the pressure applied to the diaphragm or the displacement or deformation of the diaphragm by a converting device. When this happens, the sensing device is designed so that deformation of the diaphragm is minimized so the pressure doesn't vary with the influence of the pressure source and a simple relation, such as a proportional relation, is established between the input and the electric signal. Therefore, the pressure sensor can widely detect the input but has a restriction in that a maximum deformation of about 1 mm can be read. In order to sense the pen pressure, the writing surface receiving the pen pressure has to be sufficiently hard. For this reason, in the input apparatus sensing pen pressure, an operator may write with a hard pen on a hard writing surface, and thus it is difficult for the operator to feel a pleasant, natural feeling or a comfortable operating feeling.
On the other hand, a capacitance type displacement sensor is disclosed as the displacement sensing apparatus in numerous Japanese unexamined patent application publications. The capacitance type displacement sensor is one kind of non-contact type minute displacement sensor applying the principle of a capacitor and is capable of measuring minute displacement with high precision by using a variation in the capacitance in inverse proportion to the distance between electrodes. In order to detect the minute variation in the capacitance with high precision, methods such as frequency modulation, amplitude modulation, and phase modulation may be used and a capacitance displacement sensor can detect displacement of 0.2 mm to 10 mm with a high precision of 1 μm to 10 μm.
As an input apparatus applying a displacement sensor, Japanese Unexamined Patent Application Publication No. 2005-3494 (claim 2, pages 7 to 12, FIGS. 1 to 6), which is described below, discloses a panel sensor which includes a force detecting unit detecting a force applied to a panel and in which the force detecting unit includes a detector detecting a weak force and a detector detecting a strong force.
FIGS. 7A to 7C are partial sectional views illustrating an example of the panel sensor. A panel sensor 100 generally includes a square panel 110, panel holders 120 disposed on the four corners of the square panel 110, and a force detecting unit (force sensor) 130. A force applied to the panel 110 is transferred to the force sensor 130 via the panel holders 120. FIG. 7 shows the vicinity of one corner (angled portion) of the panel sensor 100.
The force sensor 130 includes a diaphragm 131, an electrode 132, a substrate 133, an inner casing 134, a crossbeam 135, a fixed casing 136, an electrode 137, and a holder 138. The diaphragm 131 includes a thin film 131a with elasticity and a holding portion 131b holding the thin film 131a in a state where a tensile force is maintained. The diaphragm 131 is fixed along with the electrode 132 to the substrate 133. A displacement electrode (not shown) is disposed in the thin film 131a. The displacement electrode and the electrode 132 form a first capacitor. The substrate 133 is disposed on the holder 138 via the inner casing 134, the crossbeam 135, and the fixed casing 136. The crossbeam 135 is formed of a material with a predetermined elasticity. The electrode 132 and the electrode 137 on the holder 138 form a second capacitor.
When a small force is applied in a direction of pressing the panel 110, as shown in FIG. 7B, the thin film 131a is expanded and deformed and thus the displacement electrode on the thin film 131a is displaced. This displacement is detected as a variation in the capacitance of the first capacitor. When the force applied to the panel 110 becomes stronger, the distance between the thin film 131a and the electrode 132 becomes narrower and thus the capacitance of the first capacitor becomes larger.
When the force applied to the panel 110 further becomes stronger, as shown in FIG. 7C, the thin film 131a and the electrode 132 are attached to each other. Therefore, the capacitance of the first capacitor is rarely varied. In this case, since the crossbeam 135 is curved, the substrate 133 to which the electrode 132 is fixed is displaced downwardly in the drawing. This displacement is detected as a variation in the capacitance of the second capacitor.